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Forecasting indexes of dense fog formation and dissipation along highway are summarized by analyzing the meteorological element features of 84 observation samples from the traffic meteorological observation data along the Beijing Qinhuangdao Highway. The visibility during the dense fogs almost keeps unchanged. Small rise during the decline of temperature provides a good indicator of sudden visibility decreasing. The relative humidity can be up to greater than 80% in an hour before the sudden visibility decreasing. General dense fogs mostly appear during the continuous linear decreasing period of temperature after temperature fluctuation. The relative humidity can reach up to greater than 90%, which happens 15 hour before the visibility decreases to less than 500 m, and the relative humidity reaches the saturated state before the visibility decreases to less than 50 m. When fog dissipation is caused by cold air, forecast should focus on the time when the cold front reaches the highway; when fog dissipation is caused by radiative temperature rise, forecast should focus on the judgment of weather conditions and temperature increasing speed.